Later-migrating warblers have omnivorous eating habits

Sachi Schott
For the Lakeside Leader

As we approach the autumn equinox, Slave Lake is beginning to see an influx of later-migrating birds, among them myrtle and orange-crowned warblers.

A bird of many names, the myrtle warbler is technically the eastern form of the yellow-rumped warbler, whose name comes from its bright yellow backside. This distinctive field marking also gives it its other common name of ‘butterbutt’!

The name myrtle warbler, meanwhile, is derived from its habit of gorging on wax myrtle berries along the east coast. This ability to eat and digest fruit, where most warbler species depend largely on insects, allows the myrtle to migrate early in the spring and late in the fall, when conditions are too cold for insects to be numerous but berries can still be found.

There have been many days this fall when myrtle warblers have made up the bulk of the birds banded, but on Sep. 12, orange-crowned warblers outnumbered them for the first time this season. Unlike the yellow rump of the yellow-rumped warbler, the orange-crowned warbler’s eponymous field marking is rarely visible unless you have the bird in your hand – something that is only possible for trained researchers like the LSLBO’s bird banders!

Similar to the myrtle warbler, the orange-crowned is another late migrant that is more omnivorous than most warblers. In addition to insects, it will eat berries, nectar, and even tree sap, which it sips from the holes drilled by sapsuckers. Orange-crowned warblers also visit bird feeders, for fat-rich suet and peanut butter.

Sparrows and thrushes are also common migrants at the moment, and diet plays a role in the timing of their migration as well. As the seeds and berries that they rely on for fuel remain available late into the year, both groups are among the last songbirds to travel south each fall.

In total, 340 birds were banded by the LSLBO this week, bringing the fall season total to 3,768 birds of 56 species. During this same period, our owl banding program was lucky enough to capture a boreal owl! Curiously, the LSLBO has so far only ever captured this species on alternate years: in 2016, 2018, and now in 2020.

Very little is known about the boreal owl; it is only recently that the preliminary results from other banding programs have suggested that some parts of its population are migratory. The extremely sporadic success of the LSLBO’s boreal owl banding program, however, suggests that our owls are not among them. Instead, we suspect that the boreal owls we capture are young birds dispersing for the first time from the territories in which they were hatched.

Orange-crowned warbler

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